1. Field of the Invention
The present invention relates to an electronic equipment with a geomagnetic direction sensor and, more particularly, to an electronic equipment incorporating a flux gate magnetic sensor having low power consumption.
2. Description of the Prior Art
Electronic timepieces with a geomagnetic direction indicator have been known as conventional compact electronic equipment with a geomagnetic direction indicator. Such an electronic timepiece includes a compass for indicating a geomagnetic direction attached to a wristwatch band. The compass is separately mounted on the timepiece unit so that the overall arrangement is bulky. Unexamined Patent Publication (Kokai) No. 59-126285 filed by the present applicant describes an electronic timepiece incorporating a Hall element for electronically detecting a geomagnetic direction. However, geomagnetic sensitivity of the Hall element is not so good.
A flux gate magnetic sensor is known as a geomagnetic sensor having good sensitivity characteristics for electronically detecting geomagnetism (e.g., U.S. Pat. No. 3,903,610). The flux gate magnetic sensor is arranged such that an excitation coil and a sensing coil are wound around an annular magnetic core. An AC pulse signal is supplied to the excitation coil, and a signal extracted by a capacitor connected in parallel with the sensing coil is detected. The detected signal is then smoothed to obtain a DC voltage which represents a geomagnetic direction. This DC output is proportional to the cross-sectional area of the annular magnetic core. In order to produce a large output by using the flux gate magnetic sensor, the magnetic core must have a sufficiently large size and thickness. If the flux gate magnetic sensor is built into compact electronic equipment such as an electronic timepiece in association with other components, it is difficult to realize a compact system because of the spatial factor.
In a conventional direction sensor with a flux gate magnetic sensor, the period of the AC pulse signal supplied to the excitation coil must be shortened to increase the response time for direction indication, thus increasing power consumption.
Furthermore, the direction sensor using the flux gate magnetic sensor displays a wrong geomagnetic direction which is not associated with geomagnetism if a magnet having a magnetic field with a magnitude higher than that of geomagnetism is present near the magnetic field. In a location where geomagnetism is not detected, such as in a tunnel, the geomagnetism direction cannot be displayed, thus degrading reliability in use.